Cyclic process for making butadiene



rmneusazz, 1946. 2,393,331

K. Kelly and Peter J. Ferrara, Charleston, W. Va., assignors to Carbideand Carbon Chemicals Corporation,

York

it corporation oi New Application A ril at, 1944, Serial No. 532,980.

(01.260-681) y w v 11 Claims.

This invention pertains to a cyclic process for producing butadieneiroma mixture of ethanol and acetaldehyde, and to an improved method forseparating unreacted acetaidehyde in such a process for recycling.

The reaction of ethanol-with ,acetaidehyde to produce butadiene has beeninvestigated academically for many years, and the recent development ofimproved catalysts for this reaction has enabled the process to beoperated commercially. In the present state of the art, however, theknown catalysts are not completely selective,

and they also 'exerta secondary action on the ethanol and acetaldehydeto convert them to side reaction products. The principal. side reactionwhich occurs is the dehydration of ethanol to-diethyl ether. althoughother ethers, esters,

ketones. liquid hydrocarbons and higher aldehydes are also produced asthe result of more complex side reactions. y 1

The eilluent materials from the butadiene converter contain butadiene,ethanol, acetaldehyde.

water, hydrocarbon gases, and the side reaction products discussed above(hereinafter. collectively termed "by-products). Satisfactory methodshave beendeveloped for recovering butadiene from the condensiblereaction products by condensation and distillation, and the butadienepresent in the hydrocarbon gases may be recovered by scrubbing the gaseswith a solvent for. the butadiene, and removing the butadiene from thesolvent. However, the recovery of'acetaldehyde of satisiactory purityfrom the'liquid reaction products, and the removal of by-products hasproven ditllcult.

When the remainder of the reaction mixture, after expulsion of 'thebutadiene and gases, was

" introduced into a iractionating column of the continuous type,intended for the removal of acetaldehyde. which was. the most volatileconstituent present in any quantity, considerable diiilculties wereencountered. Not only did the acetaldehyde form azeotropes (constantboilin mixtures non-separable by distillation because the vapors givenof! irom the liquid have the same composition as the liquid) with thediethyl ether'and other constituents oi the by-products,

which'necessitated the recycling oi such by-. products in the quantitiesfixed by the azeotropic compositions,- but the composition of such dlstillate was not uniform. It was found that the by-products. appear inthe distillate in even -8reater quantities than called ior by the amandwater.

tropic composition at fractionating temperatures designed to separateacetaldehyde from ethanol When such by-products are recycled in largeamounts, they-cause a decreasein the production 05 butadiene throughdilution of thereactants. Furthermore, when recycled in-largequantitles, the by-products may react with ethanol or acetaldehyde,which reduces the chemical eificiency of the process. Finally, in thesequantities, some of the by-products exert a harmful action on thecatalyst, reducing its effectiveness by,

depositing carbonaceous material thereon, ne-

cessitating frequent reactivations of the catalyst and reducing itsavailability for butadiene production. I

The azeotrope of acetaldehyde with diethyl etherboils at 57 C. at 40 p.s. 1. gauge, and contains about 75% acetaldehyde by weight at theseconditions. However, special method must be adopted to remove suchazeotrope continuously from the-column, since it cannot be generated ina column for recovering acetaldehyde from the ,reaction products of thebutadiene, converter,

after separation of thebutadiene, when'the base temperature issuil'iciently higlf, about 120 C.

at a pressure 013-40 p.- s. 1. gauge, to volatilize all the acetaldehydefrom the base of the column.

' .Under' such conditionsthe by-products, including theacetaldehyde-diethyl ether aaeotrope in such 5 part, this may additionaldiethyl ether, tend to distill over with quantities that theconcentration oi'acetaldehyde in the distillate from the column has beenreduced at times to less than by weight. In

of the -by-products, because 01' their insoiubility in the mixture ofwater and ethanol at the base i of the column. When the concentration ofacetaldehyde was reduced, as indicated above, the by-productsaccumulated in the system to such an extent that it became necessary, attimes, to

purge the system by removing from the cyclev large amounts oi unreactedethanol and acetaldehyde until the purge oi lay-products was eiiected. I

By means of this invention, however. an acetaldehyde distillate of highpurity may be recovered from the products 0! the reaction producingbutadiene. The purity of this distillate exceeds the .azeotropiccomposition, and the concentration of acetaidehyde in the distillate mayexceed and may be as high as to by wellht. Accordingly, therecirculation of j by-products through the system in large quantitieswith the recovered acetaldehyde is avoided,

be caused by a 'steam distillation 'These desirable results areaccomplished by distilling the remainder of the reaction products fromthe butadiene converter, after expulsion of manner, it has been foundpracticable to separate a large part of" the water-insolublelay-products from the acetaldehyde and other water-soluble components bywashing with water. Substantial-- ly complete recovery of acetaldehydefrom the distillate may be achieved by relatively iew wash- 1118s, andthe by-products layer discharged from the washing operation containsonly negligible amounts oi acetaldehyde and ethanol; despite the factthat substantially all the unreacted acetaldehyde from the'butadienereaction is subjected to the washing operation.

When the washing operation is conducted so as to recover substantiallyall the acetaldehyde, all the by-products in the system are not removedas the water-insoluble layer discharged from the washing operation, butsuflicient amounts are removed to accomplish highly valuable objectives.

In the first place, sufllcient icy-products are removed to prevent theiraccumulation in the cyclic system. Inthe second place, the concentrationoi by-products in the column intended for removal of acetaldehyde isreduced to a quantity less than that required'for the continuousdevelopment oithe azeotropes of acetaldehyde with the by-products. Thus,at no place in the column are conditions reached where the vapor is inequilibrium with a liquid having the composition of the azeotrope. Thus,acetaldehyde vapors containing more acetaldehyde than would be fixed bythe azeotroplc compositions are generated from the column, and, incontinuous operation, an acetaldehyde distillate containing about 90%acetaldehyde by weight has been removed continu ously from the columnfor recycling over the butadiene catalyst.

The residue from the distillation to separate acetaldehyde maybereturned to the preceding column, in which by-products are removed, foradditional separation of by-products, or it may be passed directly to astill 101- recovering ethanol. The residue from theby-product stillpassesto a still for recovering ethanol.

In washing the distillate containing the acetaldehyde and by-products,the use of a minimum amount or water will avoid handling increasedquantities of water in the subsequent ethanol still and will-avoid thesolution of large quantities oi the by-products in the mixture of water,acetaldehyde and ethanol. The use of larger amounts by weight is removedthrough pipe 2|.

or water will efiect a greater recovery of acet- .ings.

distillate by weight which is to be washed, it is suitable to use, ingeneral, from 0.5 to 2.0 volumes of water per volume of distillate. Whenthe ratio of water to distillate of such acetaldehyde concentration isabout 0.65 by volume, the ratio of the bottom aqueous layer to the topoil layer is about 4.4 by volume, and the concentration by weight ofacetaldehyde in the oil and aqueous layers is in the ratio of 1.33 to1.0 at C. At 30 to 35C., the ratio is approximately unity, so that thewashing is more efiective at lower temperatures. Washing at lowertemperatures requires means to remove the heat evolved by the solutionof acetaldehyde in water, in order to maintain the desired temperature.Also, it is frequently desirable to use as the washing liquid,discharged aqueous scrubbing liquid from scrubbers elsewhere in thesystem designed to recover acetaldehyde from butadiene and vent gases.Such scrubbing liquid may contain from 1 to 2% acetaldehyde by weight,and it is frequently somewhat heated. Substantially all the acetaldehydemay be recovered from the top layer in not more than two to threeadditional wash- The nature of the cyclic process, and suitableconditions under which it may be practiced, may be illustrated withreference to the drawing.

Ethanol and acetaldehyde vapors, for example in the molar ratio of about3 to 1, respectively, are passed to a converter 10, which contains acatalyst of an appropriate type at a temperature of about 300 to 350 C.Suitable catalysts are described in United States application Serial No.460,120 filed September 29, 1942, by W. J. Toussaint and J. T. Dunn.Part of the ethanol and acetaldehyde is converted to butadiene in thepresence of the catalyst, and the eiliuent vapors pass through pipe IIto a condenser l2, where the less volatile constituents are liquefied,and

- withdrawn through pipe I3 to distillation column H, to recover thecondensed butadiene. The gases leaving the condenser are compressed to apressure of about p. s. 1. gauge, and pass through a condenser l Band aseparation tank It through pipes l1 and 18 respectively. More of thecomponents, including additional amounts of butadiene, are-liquefied bythis process and pass through pipe I! to distillation column is. Theuncondensed gases are withdrawn through pipe 20, and butadiene andacetaldehyde may be recovered from such gases by scrubbing them with asolvent, such as ethanol.

From the distillation column ll, on which is maintained aheadtemperature of about 47 C. at p. s. 1. gauge, butadiene vapor of aboutpurity and containing about5% acetaldehyde Part of the butadiene iscondensed in condenser 22, and returned through pipe 23, asreflux forthe column. The remainder of the butadiene passes to a scrubbing tower2|, wherein acetaldehyde is separated from the butadiene by scrubbingwith water introduced through pipe 20. Butadiene of about purity isremoved through pipe'26 for further purification.

The residue from column l4, containing acetaldehyde, ethanol, water,diethyl ether and other by-products passes through pipe 21 todistillation column 28. This column is operated-under such conditions asto remove substantially all the acetaldehyde in the-teed,together with alarge traction of the by-products. Atypical analysis I asoassi.

\ o! the overhead vapor from such column is as 1011M: v I i pacificgravity; 0.800 2072c c.

, Component Amount Per eentby 1 might Aeetaldeh dc v 53. Ethel-s comnounds boiling below 40 0. exclusive oiacetaldehy 16.0 Ethyl acetat 7.0Ethan 13.0 "Oilsfl-complex mixtures. 6. 6 Water 2.0 Higher aidehydes 2.

The ethanol content of such vapor is kept low by maintaining a headtemperature of 68 to 72 C. under a pressure of 22 to 23 p. s. 1. gaugeand a reflux ratio oi!- 2.5 to 1. Higher reflux ratios may be-employedfor this purpose, the upper valuebeing fixed by the permissible downflowin the column. ,The acet'adehyde distilis as a complex mixture,including azeotropes, with'diethyl ether and other lay-products,asindicated above, and the distillate is removed through pipe 29 tocondenser where the distillate is liquefied. Part of the distillate isthen returned through pipe 3i as reflux to column 28,- and part issubjected to a washing operation to remove suiiicient byproducts toprevent the formation of azeotrcpic compositions in the column whichrecycles acetaldehyde vapor to the butadiene converter and to permit therecovery oi acetaldehyde or satisiac tory purity by distillation. Forthis purpose the condensate is, mixed in pipe 9 with the scrubber liquidirom the scrubber 2| and pipe 32 which contains about 1 to 2%acetaldehyde by weight,

and passes to a tank'--iI, -where the mixture separates into an upperand lower layer. The use of the aqueous scrubber liquid to effectseparation of the mixture is not essential, but affords econ- 3 throughpipe as to the same distillation column,

or it may be recirculated through the washin Y operation by means oipipe 44 and by-paas valve only in the heat required in subsequentdistillations. When the volume ratio of water to .distil late is 0.65,the ratio at lower layer to upper layer is 4;.3 by volume, and theconcentrations by weight of acetaldehyde in the lower layer is 30%. and.40% in the upper layer. The upper layer is washed again with one-haltits volume of water introduced through pipe 35 to pipe 3|, and separatedinto layers in tank 38. The ratio of bottom layerto top layer, is 1.27by volume, and the respective concentrations of acetaldehyde in the topand bottom layers are 30% and 22%. by weight. Tanks 83' and I6 should'beconstructed to withstand at least a pressure of 20 p. s. 1. gauge at. C.The top layer from tank 38 passes through pipe 81 to an extractor 38containing a suitable packing, whe re it is continuously washed withabout an equal volume of water to extract -In a large scale operationthe following data have been obtained on the washing operationdescribed, the quantities being expressed in pounds per hour: v

First wash Dlstil- Wash Bottom Top layer late liquor layer #1 i iiAcetaldeh de 7, 075 i, 635 Higher al ehydes 206 160 Diethyl ether 900Ethyl acetate 845 see r "811s" n4 sec Aldehyde recovery, gross, 80.7%.

Second wash Top Wash Bottom Top layer layer #1 liquor layer #2 #2Acotaldeh de. l, 423 242 Higher al ehydes .53 107 Diethyl admin... 708l, 197 'Ethyl acetate 333 362 Ethanol 124 30 W ater 7, 652 64 "0115 132648 v s, 410 1, s00 10, 420 2. s50

Aldehyde recovery in two washes,vgroes, 06.5%.

' Third wash (extraction) Top Wash Bottom I Top I layer #2 liquor layerI3 layer 13 Acetaldehydall m 256 31 Higher aldehydes 107 41 66 Diethyleth l, 107 232 965 Ethyl acetate 362 70 292 Ethanol. 30 11 10 Water. 64-2, 630 9 0ils" 548 6 542 2, use 3, 24s 1, sec

Aldehyde recovery in three washes, gross, 99.3%.

Instead of the batch washing process described,

acetaldehyde. The ratio of the lower aqueous 6 layer to the upperby-produet layer is 2.1 by voltune. and the aldehyde concentrations are20% in the aqueouslayer by weight and 4% 1nthe byproduct layer. i n hydeis about 99.5%, and less acetaldehyde is discarded from the system bymeans oi this process than when an attempt is made to separate'theby-products by fractionation and subsequent batch distillations, becauseofazeotropes which form.

The lower layers from tanks 33 and 36 pass through pipes 40 and IIrespectively to column 42, intended for removal of acetaldehyde. The

aqueous phase from the extractor, l8 may'pass The gross recovery ofacetalderate the azcetaldehyde from the by-products. The following datahave been obtained in an extractor 14 inches in diameter, 20 feet highand having the middle 15 feet packed with 1 inch porcelain rings;

Continuous phase Water Distillate Distiliatarate,lb.lhr l...l.. 1,1901,730 Water, lb./hr 2, an 2, 330 ,Top layer, lbJhr. m 1!!) Bottom layer,lb.lhr. 3, 918 3. 930 Per cent acetaldehyde in distillate 4s. 0 52 Percent acetaldehydc in top lsye i.- l0. 5 6. Per cent acetaldehyde inbottom laye 11.0 22. Per cent recovery of acetaldehyde 97. 5 09.

In this particular embodiment of the invention,

' so that the principles of the invention are the same, irrespective ofthe source of theacetaldehyde consumed in the process. Thus,thecomposite feed to the column 42 may contain:

. Per cent by weight Acetaldehyde 21.1 Ethanol 6.5 By-products 5.1 Water67.3

, the. column. This vapor is led through pipe 41 for passage through thebutadiene converter. Part of the vapor is condensed in condenser 48 andreturned as reflux through pipe 49. Should acetaldehyde be obtained froma source ther tha ethanol, as from acetylene, the acetaldehyde consumedin the process may be added as reflux in the column.

The residue from the acetaldehyde still 42 may be recycled to column 28through pipe 50 torturther removal of by-products, or, by means of valve5| and pipe 52, it may be. passed directly to a column 53 for recoveringethanol. The residue from the by-products column 28 also passes throughpipe 52 to the ethanol still 53.

lows, when both residues are passed directl to column 53.

Acetaldehyde Ely-product The ethanol still may operate at a pressure of50 p. s.'i., and a head temperature oi. 120 C.

and ethanol vapor is passed through pipe 54 to the butadiene converter.Where the butadiene reaction is operated in conjunction with a processfor producingacetaldehyde from ethanol, part of the recovered ethanol isrecycled to produce consumed in the processmay'be added through pipe 55as part of the refluxrequired in the ethanol column. as described inUnited States Patent No. 2,249,847 to I. L. Murray. Additional refluxmay be supplied by condensing part of the overhead vapor in condenser58, and returning the condensate to the column through pipe 51. Water isdischarged from the column through pipe 58.

and its heat content may be recovered by suitable 70 heat exchange inthe system.

By means 01' the invention described, it has proved possible to removethe by-products as they are formed in the reaction oi acetaldehyde withethanol, and to prevent their accumulation in the hyde distillate. Thisreduction oi recirculated impurities has-led to an increasedproductionot' butadiene and has avoided a source of catalystcontamination. A minimum amount of ethanol and acetaldehyde is discardedwith the by-products, which increases the chemical efliciency of theprocess for making butadiene. We claim: I v

1. In a cyclic process for making butadiene which comprises passingacetaldehyde and ethanol over a catalyst to form a mixture includingbutadiene, unreacted-acetaldehyde, and byproducts, the steps'of removingbutadiene from said mixture and distilling the mixture, after expulsionof the butadiene, to remove a distillate containing acetaldehyde andby-products, mixing said distillate with water to partition it betweentwo immiscible phases of different specific gravities, distilling thephase having the higher specific gravity to remove a fraction containinga higher concentration of acetaldehyde than said distillate, andrecycling this fraction over the catalyst.

2. In a cyclic process for making butadiene which comprises passingacetaldehyde and ethanol over a catalyst to form a mixture includingbutadiene, unreacted acetaldehyde, and byproducts, the steps of removingbutadiene from Typical compositions of such residues are as folsaidmixtureand distilling the mixture. after expulsion of the butadiene, toremove a distillate hyde than said distillate, and recycling thisfraction over the catalyst.

3. In a cyclic process for making butadiene which comprises passingacetaldehyde and ethanol over a catalyst'to form a mixture includingbutadiene, unreacted acetaldehyde, and byproducts, the steps of removingbutadiene from said mixture and distilling the mixture, after expulsionoi the butadiene, to remove adistillate containing acetaldehyde and,by-products, mixing said distillate with water in separate increments topartition it between two immiscible phases of difierent specificgravities, distilling the phase having thehigher specific gravity toremove a i'raction containing a higher concentration of acetaldehydethan said distillate, and recycling this fraction over the-catalyst.

4. In a cyclic process for making butadiene which comprises passingacetaldehyde and ethanol overa catalyst to form a mixtureincludproducts, the steps of removing butadiene from said mixture anddistilling the mixture, after exadditional acetaldehyde. In any event.ethanol pulsion oi the butadiene, to remove. a distillate containingacetaldehyde and by-products, countercurrently extracting saiddistillate with water to partition it between two immiscible phases ofdifferent. specific gravities, distilling the phase having the higherspecific gravity to remove a fraction containing a higher concentrationof acetaldehyde than said distillate, and recycling this fraction overthe catalyst.

5. In acyclic process for making butadiene which comprisespassingacetaldehyde and eth anol over a catalyst to form a mixture includingbutadiene, acetaldehyde. ethanol. diethyl ether and" other lay-products,the steps of removing butadiene from said mixture and disthe mixture,after expulsion of butadiene,

aaaase to remove a distillate containing a moderately high percentage ofacetaldehyde and lesser amounts oi. by-products and ethanol, mixing saiddistillate with water in successive steps to separate it intowater-miscible components and water-immiscible component's, distillingthe water-miscible components to remove a fraction having a higherconcentration of acetaldehyde than said distillate, and recycling thisfraction.

over the catalyst.

6. In a cyclic process for making butadiene which comprises passingacetaldehyde and ethanol over a catalyst to form a mixture includingbutadiene, unreacted acetaldehyde, and byproducts, the steps of removingbutadiene from said mixture and distilling the mixture, after expulsionof the butadiene, to remove a distillate containing acetaldehyde andby-products', mixing said distillate with water to partition it betweentwo immiscible phases of different Specific gravities, distilling thephase having thehigher specific gravity to remove a fraction containinga higher concentration of acetaldehyde than the azeotrope ofacetaldehyde and byproducts, and recycling this fraction over thecatalyst.

'7. In a cyclic process for making butadiene which comprises passingacetaldehyde and ethanol over acatalyst to form a mixture includingbutadiene, unreacted acetaldehyde, and byproducts, the steps of removingbutadiene from said mixture and distilling the mixture, after expulsionof the butadiene, to remove a distillate containing substantially 'allthe acetaldehyde and a large portion 01- the by-products present in saidmixture, mixing said distillate with water to-partition it between twoimmiscible phases of difierent specific gravities, distilling the phasehaving the higher specific gravity to remove a fraction containing atleast about 85% acetaldehyde by weight and recycling this fraction overI the catalyst.

8.-"ina cyclic process for making butadiene which comprises passingacetaldehyde and ethanol over a catalyst to form a mixture includingbutadiene,-unreacted acetaldehyde, and byproducts, the steps or removingbutadiene from said mixture and distilling the mixture, atter expulsionof the butadiene, to remove a distil- I late containing acetaldehyde andby-products, mixing said distillate with water to partition it betweentwo immiscible phases of difierent specific gravities, distilling thephase having the higher specific gravity to remove a fraction containinga higher concentration of acetaldehyde than said distillate. recyclingthis fraction over thecatalyst,andreturningtheresidueiromthis lastdistillation to the previous distillation.

v 5 9. In a cyclic process for making butadiene which comprises passingacetaldehyde and ethanol over a catalyst to form a mixture includingbutadiene, acetaldehyde, ethanol, and byproducts, the steps of removingbutadiene from said mixture and distilling the mixture, after exanolover a catalyst to form a mixture including butadiene, acetaldehyde,ethanol, and by-products, the steps, of heating such mixture to expelbutadiene vapors and a portion of the acetaldehyde, washing said vaporswith water to form a dilute aqueous solution of acetaldehyde, distillingthe remainder of said mixture, after expulsion of butadiene, to remove adistillate containing acetal'dehyde and lay-products, mixing saiddistillate with said aqueous solution to partition the distillatebetween two immiscible phases of different specific gravities,distilling the phase having the higher specific gravity to remove, afraction containing a higher concentration of acetaldehyde than saiddistillate and recycling the traction over the catalyst.

11. In a cyclic process for making butadiene which comprises passingacetaldehyde and ethanol over a catalyst to form a mixture includingbutadiene, acetaldehyde, ethanol, and by-products, the steps of heatingsuch mixture to expel butadiene vapors and a portion or theacetalderecycling the fraction over the catalyst.

hyde, washing said vapors with water to iorm a dilute aqueous solutionof acetaldehyde, distilling the remainder of said mixture, atterexpulsion of butadiene, to remove a distillate containing acetaldehyde andlay-products, mixing said distillate with saidaqueous solution topartition the distillate between an aqueous layer and a non-aqueouslayer, mixing the non-aqueous layer with water to distribute it betweena second aqueous layer and a second non-aqueous I layer, and distillingthe two aqueous layers to remove a fraction containing a higherconcentration of acetaldehyde than said distillate and HARTSELLE D.KINSEY. THEODORE H. KELLY. PETER J.

